feat(rollbar): add Rollbar plugin (#832)

* Add Rollbar plugin

* Add documentation

* Add return type to init function

* Remove init params

src/plugins/rollbar.ts

@@ -0,0 +1,33 @@
+import { Plugin, Cordova } from './plugin';
+
+/**
+ * @name Rollbar
+ * @description
+ * This plugin adds Rollbar App monitoring to your application
+ *
+ * @usage
+ * ```
+ * import { Rollbar } from 'ionic-native';
+ *
+ * Rollbar.init();
+ *
+ * ```
+ */
+@Plugin({
+  pluginName: 'Rollbar',
+  plugin: 'resgrid-cordova-plugins-rollbar',
+  pluginRef: 'Rollbar',
+  repo: 'https://github.com/Resgrid/cordova-plugins-rollbar',
+  platforms: ['Android', 'iOS'],
+  install: 'ionic plugin add resgrid-cordova-plugins-rollbar --variable ROLLBAR_ACCESS_TOKEN="YOUR_ROLLBAR_ACCEESS_TOKEN" --variable ROLLBAR_ENVIRONMENT="ROLLBAR_ENVIRONMENT"'
+})
+export class Rollbar {
+
+  /**
+   * This function initializes the monitoring of your application
+   * @return {Promise<any>} Returns a promise that resolves when the plugin successfully initializes
+   */
+  @Cordova()
+  static init(): Promise<any> { return; }
+
+}